The effects of pressure on cochlear microphonics in experimentally induced hydropic ears in the guinea pig.

The effect of perilymphatic pressure on the cochlear microphonics (CM) threshold was examined in guinea pigs with experimentally induced hydrops. When a pressure of 300 mm H2O was applied to the scala tympani of the basal turn, the 500 Hz CM threshold shifts in ears during the 1st week following obliteration of the endolymphatic sac and duct were significantly smaller when compared with shifts in normal ears. Larger threshold shifts were then regained at 4-12 weeks after surgery. When acetazolamide was administered to hydropic animals, the effect of the increase of perilymphatic pressure on the CM threshold was also investigated. During the 1st postoperative week (4-7 days after surgery), CM threshold shifts were larger when compared to changes in hydropic animals without medication. The CM depression as the result of pressure is probably due to a mechanical effect on the intracochlear partition.